The doc you mentioned is the "one and only" complete security guideline for the automation system by DC-AE. It will be updated from time to time.
In the end, SAFEX-C will be integrated as well, I guess.
In the meanwhile it is unlikely, that a SAFEX-C isn't part of the machine network and very often behind firewall's etc. It isn't an "edge"-device. So make sure, that you establish proper security measures by yourself / design of the network.
Remark: I'll pass your question to the resp. DC-AE persons, internally.
